银基中间层连接AZ31镁合金的界面行为研究

Research on interface behavior of brazed joints of AZ31 magnesium alloy using Silver-base alloy interlayer

摘要:

为了改善AZ31镁合金钎焊接头的组织状态和润湿性能，用银基合金AgCuZn做中间层，在不使用钎剂的条件下，采用接触反应钎焊的方法对AZ31镁合金进行连接。结果表明：在500℃保温时间为15min的条件下，中间层完全溶解，搭接处形成了一个完整的无缺陷的钎焊接头。金相分析结果显示：钎缝表现为多元共晶组织形态，粒状和短棒状的第二相均匀的分布在连续的基体上，钎缝中心区有少量浮云状初晶。XRD及EDS分析表明：钎缝中的第二相是富含Ag、Cu、Zn的α-Mg固溶体，基体相主要是化合物AgMg3和少量CuMgZn。搭接接头的平均抗剪切强度是108.9MPa，拉伸剪切断口能清晰看到冰糖状颗粒和解理台阶，表现出沿晶断裂和穿晶断裂的混合断裂特征。中间层的加入影响了接头的组织形态和力学性能。

Abstract:

Contact-reaction brazing is used to bond AZ31 joints in order to improve the microstructure and wettability of AZ31 magnesium alloy brazed joints. This is achieved by using an AgCuZn interlayer during the brazing process without the use of a flux. The results show that a defect-free brazed joint can be obtained when the AgCuZn interlayer is completely dissolved at 500 °C for 15 minutes. The microstructure in the brazing seam consisted of multiple eutectic structures. The second phase was composed of granular and short rod-like features. Both the granular and the short rod-like structures were uniformly distributed in the continuous matrix. A small amount of primary crystal taking on cloud state is present in the brazing seam center. X-ray diffraction and energy spectrum analysis indicate that the second phase consisted of an α-Mg solid solution containing high amounts of Ag, Cu, and Zn, while the basal body consisted of an AgMg3 compound and small amounts of CuMgZn compound. The mean shear strength of the brazed joints was about 108.9 MPa. Both sugar granules and cleavage steps were clearly observed in the tensile shear fracture morphologies with mixed fracture characteristics in both intergranular fractures and transgranular fractures. The AgCuZn-base interlayer influenced the microstructure and mechanical properties of the brazed joints.